Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

3.6- Etheno bridge

Diaz and coworkers have investigated the solvolysis of a related system 70 in which, however, the 3,6-methano bridge of the nortricyclyl system is replaced by a 3,6-etheno bridge. Relative rates are given for hydrolysis in 80 % aqueous acetone at 100 °C. Products... [Pg.662]

The activation energy for rotation about the terf-alkyl-to-triptycyl bond was 36.6 kcal/mol for 101, and the frequency factor was 10 7 sec 1. It should be noted that the barrier to rotation is raised by ca. 4 kcal/mol by going from a bis(methoxycarbonyl)etheno bridge to a benzeno bridge. The equilibrium constant ( sc/ap) was 2.0, as expected on statistical grounds. [Pg.57]

Reduction of the 6,14-e G o-etheno bridge further enhances potency, for example (Vila) (3 200) and (Villa) (11 000), the latter alcohol being the most potent analgesic so far reported. [Pg.234]

Peroxydisulfate was also reported as a reagent in nucleoside chemistry. Interestingly, the etheno bridge of l,V -ethenoadenosine can be smoothly removed by treatment with potassium peroxydisulfate (equation 20). ... [Pg.1011]

Reaction of benzyne with arsabenzene affords l,4-etheno-l,4-dihydro-l-arsanaphthalene (192) from which an etheno bridge can be removed with 3,6-di(2-pyridyl)-l,2,4,5-tetrazine (184) to afford, via the polycyclic intermediate (193), the arsanaphthalene (194) (79CC880). [Pg.553]

Etheno bridge inserted between positions 6 and 14 rings, plus hydroxy, trimethyl propyl substitution on position 7. [Pg.391]

Reduction of the 6,14- endo-etheno-bridge results in further enhancement of potency. For etorphine the potency becomes 11,000 x morphine, one of the most potent analgesics to have been reported. [Pg.81]

On the other hand the cycloaddition of 4-phenyl-3//-1,2,4-triazole-3,5(4/7)-dione to a known mixture (E,E)-. (E,Z)- and (Z,Z)-5,6-bis(deuteriomethylidene)bicyclo[2.2.2]oct-2-ene affords a mixture of diastereomeric adducts 8 in excellent yield. A 95 5 ratio of endojexo addition was calculated from H-NMR NOE measurements, that is, attack of the dienophile takes place preferentially syn to the etheno bridge (from below the plane of the molecule)4. [Pg.1001]

The homosemibullvalenyl system(81) is in reality a 5,7-etheno bridged bicyclo[4.1.0]hept-3-en-2-yl derivative Its rate of hydrolysis has been measured in 80 %... [Pg.667]

The Diels-Alder reaction of thebaine with various electrophiles yields compounds (Fig. 7.19) that have extremely high potencies, over 1000-fold higher than morphine in some cases (see Refs. 370, 371). X-ray (372) and NMR (373) analysis of 19-propylthevinol, the 3-methyl ether of etorphine (42 above), indicates that the 6,14-etheno bridge is held inside (endo) the tetrahydrothebaine ring system and below the plane (a) of the Cy-Cg bond (see Fig. 7.19 and Ref 283) the C ring is held in a boat conformation by the 6,14-endo etheno bridge. [Pg.370]

We then attempted to clarify the reaction mechanism of this novel rearrangement. When the olefin 119 was treated with TfOH (2.2 equiv.) in toluene under reflux, the objective lactone 114 was obtained in quantitative yield (when the 7-methylidene derivative with a 6,14-etheno bridge was treated with perchloric acid, another product was obtained [104]). Next, treatment of the olefin 119 with a... [Pg.229]

AhyiH was measured in acetic acid solution. Solvent effects are significant for the alkenes and may cause the measured enthalpy changes to be — 0.7 kcal mol 1 less exothermic than the gas-phase values. This compound has juxtaposition between the methano and etheno bridges. [Pg.114]

The 7-amino-compound (139) has been rearranged through the carbonium ion to the saturated ketone (140), with migration of the etheno-bridge. ... [Pg.131]

Formally, higher oligoquinanes can be formed from fulvene 1 by consecutive addition of etheno bridges (Scheme 1 a). This concept has actually been successfully applied in the synthesis of pentalene 2 but it is unlikely to be practicable for higher members of this family due to the drastical increase in ring strain on going from, e.g., 2 to 3. Therefore all realistic approaches towards compounds 3-7 start from a less unsaturated skeleton and try to introduce the additional double bonds in a stepwise fashion (e. g. 3 8 or 9 10, Scheme 1 b). [Pg.139]

The red shifts observed for the etheno-bridged cyclophanes (21 and 22) are much stronger they reach 6500 cm-1 in 21 and the enormous value of 10,500 cm-1 in 22. Fluorescence red shifts of this magnitude usually are observed only in charge-transfer complexes between donor- and acceptor-substituted arenes (46). The spectroscopic difference of 4000 cm-1 between the isomers 21 and 22 corresponds to about 11 kcal/mol (47 kj/mol). Because no phosphorescence could be detected for all the naphthalenopyridino-phanes, the excited triplet states could not be investigated by ODMR techniques (48). [Pg.352]


See other pages where 3.6- Etheno bridge is mentioned: [Pg.677]    [Pg.79]    [Pg.291]    [Pg.291]    [Pg.291]    [Pg.292]    [Pg.292]    [Pg.293]    [Pg.311]    [Pg.48]    [Pg.230]    [Pg.406]    [Pg.298]    [Pg.537]    [Pg.124]    [Pg.38]    [Pg.28]    [Pg.537]    [Pg.70]    [Pg.80]    [Pg.81]    [Pg.233]    [Pg.146]    [Pg.34]    [Pg.233]    [Pg.474]    [Pg.114]    [Pg.8]    [Pg.334]    [Pg.338]    [Pg.349]   
See also in sourсe #XX -- [ Pg.662 ]




SEARCH



Elimination etheno bridges

© 2024 chempedia.info